This invention relates generally to hollow articles having a tubular portion (such as pipes, fittings, vessels, heat exchangers, bottles, containers, casings, cans, drums, etc.). Particularly it pertains to that portion consisting of an essentially smooth wall braced with a plurality of continuous projections like ribs and fins oriented substantially transversely to the longitudinal axis of said portion.
Such tubings are disclosed in many patents, for example U.S. Pat. No. 4,168,618 illustrates, inter alia, Y- and T-finned metal tubes for heat exchangers, U.S. Pat. Nos. 3,891,007 and 4,362,187--thermoplastic ribbed tubes.
A composite tube comprises two coaxial tubes with intermediate fins (an internally finned tubing, or a pipe with internal fins). The fins are attached by means of a mechanical tension or a metallurgical bond (soldering, brazing, etc.).
In heat exchangers, finned pipes meet high temperature requirements, improve heat exchange (because of the increased surface) and can have unique configurations, such as unusual compound bends, serpentine, spiral and helical coils. The materials for these tubings are stainless steel, copper, hastelloy, copper-nickel, admiralty, incoloy, aluminum, titanium, carbon and low alloy steel, etc. The applications of such heat exchangers include home appliances, air preheaters, steam condensers, oil coolers, generator coolers, tank heaters, heat recovery units, aerospace, cryogenic exchangers, home heating and cooling, industrial heat exchangers, immersion heaters, intercoolers and aftercoolers for air compressors, gas compressors and gas turbines, etc.
With the advent of agriculture, railroads, highways, airports, athletic fields, stadiums, recreational grounds and residential construction, plastic pipes have become increasingly important.
Subsurface drainage becomes the key to successful farming. It improves considerably the economic return of farm land, gives significantly higher and more reliable crop yields, permits farming of the land once considered unfit or unprofitable for agriculture, allows the planting season to start 2-3 days earlier (which leads to 10-25% increase in yields over undrained land), and in a wet year, can make the difference between a crop failure and success.
In farming, corrugated pipes are used for subsurface field drains (laterals and collector mains), for culverts (entrances and ditch crossings), subsurface irrigation and grain storage aeration.
Prior to plastic pipes, handling, shipping and installation of drainage systems were expensive and time-consuming. Metal culverts, clay and concrete tiles commonly used for this purpose required the piecing together of the large number of relatively short individual lengths (that is why such systems were vulnerable to misalignment) with extreme care to avoid breakage of the comparatively brittle tile material. Freezing and large farm machinery placed on the soil above the drainage tile may result in high compressive stresses. Not having effective deflection, such a tile must possess an extremely elevated load bearing strength resulting also in heavy weight. The fractured tile allows soil to enter the drainage system and at best decreases its capacity.
Until the soil fills in the void underneath the round tile, there may also be a subsequent shifting and misaligning of the tiles. This can lead to excessive soil falling between the drainage tiles and clogging or hampering the capacity of the drainage system. Also, shifting and changing contour of the supporting media require optimum flexibility.
Further disadvantages of the ceramic tile are its rigidity requiring elbows and high weight prohibiting its manipulation by an individual.
Plastic pipes, in contrast, deflect without harmful effects (the effective load bearing strength being greatly increased), are light and flexible, but strong, easily installed, shipped, stored and handled, abrasion resistant, do not corrode, rot or rust, are not affected by alkaline or acidic conditions and have good cold weather characteristics after installation below grade. Moreover, the material used is virtually nondestructive by shifting and is less expensive.
In comparison with smooth pipes, the ribbed tubings are added in strength and load bearing capacity by the projections, and negotiating curves without elbows or other fittings. This allows the use of such pipes even for small contractors and residents.
At first glance, it might appear that a light weight thin-walled ribbed plastic pipe cannot be specified for the drainage structures with severe strength requirements and adverse installation conditions because of its flexibility. However, it is the latter that allows to sustain exceedingly heavy loads. Since under external loads the pipe is considerably deflected outward, it is restrained by the surrounding soil when buried. Consequently, the passive resistance of the soil equalizes and distributes the external pressure around the pipe. That is why such a buried pipe can support large loads on the ground.
The light weight of such plastic pipes reduce operator fatigue, increase productivity, allow their transportation into areas inaccessible to trucks with heavy clay or concrete pipes and can even be manhandled.
Thus, the finned tubing is stronger, than the smooth one of the same weight and diameter, or lower in weight if it is of equal structural strength. Since the cost is essentially proportional to the weight per length, the finned tubing is many times cheaper. Also, smooth pipes, being longitudinally stiff, work as a beam, whereas finned pipes, being longitudinally more flexible, easily conform to the trench. Furthermore, more flexible circular cross-sections of the pipe develop a sidefill support of an envelope (a crude masonry arch) and should not be as strong as the stiff pipe.
In residential and commercial construction, drainage tubing is used for exterior and interior of foundation, underslabs, downspout run-offs, yard and lawn low spots, basements and window wells, driveways, sidewalks, parking lots, septic tank leach fields, driveway culverts. Finned tubing can be also used for underground utility line conduits, underslab airducts, sludge composting and aeration.
In residential and commercial foundation drainage, such tubing placed under the slab inside and around outside the basement or foundation carries off ground water preventing frost damage and basement slippage. The drainage tubing placed under patios, sidewalks and driveways helps during freeze-thaw cycles.
In foundations with high water table and rains, exterior (and some times, interior) foundation drains are placed below the level of the lowest floor to collect channel water away from footers and basement walls to a suitable outlet.
Downspout run-off plastic drains discharge water collected in the roof gutters into storm sewers, the curb at the edge of the street, etc.
In a basement window well, plastic drain pipes dispose rainwater and prevent it from seeping down the foundation into the basement.
Driveway and sidewalk plastic underdrainage prevents frost damage and pavement deterioration by stabilizing its base.
In low-spot drainage of lawns and yards plastic tubing collects and carries water to a storm sewer or other disposal means.
The outstanding performance and labor-saving of ribbed plastic tubings allow to replace metal conduits in the protection of communication and power lines (fiber optics and cables) in control boxes and panels, machinery, vehicles, buildings, constructions, above and in the ground, in walls, ceilings, floors, in indoor, outdoor and damp applications (greenhouses, laundries, etc.), in corrosive atmospheres, even in exposed forms where not subject to physical abuse, usually up to 600 volts.
Such plastic products provide an optimum balance of toughness, strength, crush and impact resistance, superior environmental stress cracking immunity, a low friction coefficient, a minimum drag during cable insertion, longer pulled-in-place lengths, light weight, flexing and bending (even at low temperatures). This allows easy handling, adaptation to other systems, inserting the tubing into an outerduct or communication lines inside it and assembly in a confined space, the necessity of elbow fittings being frequently eliminated. There are no fatigue, rust, rot, pit, corrosion or reaction to oil and surrounding soil (wether acid, alkaline, wet or dry), no jagged edges causing injuries.
Although such pipes are mostly flame retardant, self extinguishing and do not support combustion, it is admitted that burning plastics is hazardous and gives off, among other things, hydrogen chloride (a corrosive gas, lethal in high concentrations). However, noncombustible metal conduits are even worse in this respect because of possible electrical short circuits (as a result of improperly grounded metal conduits or fire during which metal conducts the heat to the cable insulation).
In utility installations, plastic tubing is used for water conduits, house drainage systems and septic tanks.
The pipes with openings (usually cylindrical holes) much larger than in drainage systems are used as a drainage pipe with a septic tank leach bed. Such a pipe is most applicable for the dispersal of wastewater effluents from septic tanks, sewage treatment plants, farm waste treatment lagoons, etc. into the ground through a system of soakage trenches.
Since radial projections prevent kinking, ribbed plastic tubings are used as inhaler tubes, respiratory pipes, gas masks and oxygen helmet tubings in medical and personal equipment.
Also, finned polytetrafluoroethylene, nylon, polyester and polypropylene tubings are used (instead of woven or knitted fabrics) as vascular graft prostheses replacing arteries and veins. Such a prosthesis is chemically inert to body fluids, body- and blood-compatible, non-carcinogenic, non-antigenic, resistant to mechanical deterioration, collapse and crushing, have good suture holding characteristics and conformability for fitting the exact anatomical position without occlusive kinking or pinching from external pressure (the ribs permitting the graft to be bent without kinking and blocking the blood flow). This pipe is capable of being sterilized, is easily implantable and has a uniform porosity allowing (without the blood leakage) tissue ingrowth from the outside and diffusion through the wall for nourishing the neointima on the inside surface.
Flexible plastic hoses solve many problems of ductwork installation: vibration dampening, connecting rigid ducts and equipment, compensating for misalignment between rigid duct ends, absorbing length changes in rigid ducts due to temperature variations, serving as removable elbows in runs of rigid ductwork, etc. That is why such pipes have found applications in ducts for duct collection, gravity drops and feeds, handling air and airborne particles and materials, street cleaning, leaf loading, sawdust, wood and metal chip collecting, rock dust exhausting, fumes exhausting, grain and flour dust handling, aeration for grain storage, plastics processing, etc.
Ribbed plastic tubing is utilized as a vacuum cleaner hose and similarly in swimming pool equipment. Here the required flexibility, small resistance to turning, withstanding the crushing effect of being stood upon or shut in a door, high resistance to collapse when looped and pooled, cannot be met by smooth pipes.
Cold and hot metal pipes are insulated with longwisely splitted snap-on plastic tubings without any adhesives, air pockets between the latter and the pipe imparting the insulating effect. This protects hot water pipes from heat loss and prevents condensation on and resultant dripping from cold water pipes. One or several concentrically mounted tubings can be used for better protection. Also, such a tubing can be used as a cover over regular insulation.
Among other numerous applications, the following should be mentioned: highways and roads (berm and roadway underdrainage, culverts), railroads (railbed and roadway-crossing drainage, switching yard underdrainage and culverts), airports (runway, underdrains, collector drains, site subsurface drainage and culverts), engineering structures (dams, levees and toe drains, dredge spoil dewatering), mining (sand, gravel and coal pile underdrainage, air ducts, water removal), golf courses and athletic fields (field, running-tract and golf-course drainage).